1. Field of the Invention
The present invention relates to a method for preparing a lithographic printing plate not requiring dampening with water which comprises a silicone rubber layer as an ink-repellent layer. The method of the present invention is capable of developing a presensitized lithographic printing plate for use in preparing lithographic printing plate not requiring dampening with water in excellent development quality with easy maintenance and less wastage of developing equipment.
2. Prior Art
As lithographic printing plates not requiring dampening with water which have a silicone rubber layer as an ink-repellent layer, there have been known, for instance, those disclosed in Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J.P. KOKOKU") Nos. Sho 46-16044 (U.S. Pat. No. 3,511,178), Sho 54-26923 (U.S. Pat. No. 3,894,873), Sho 55-22781 (=Brit. Pat. 1,419,643), Sho 56-23150 and Sho 61-616 (U.S. Pat. No. 4,358,522). A presensitized original plate for use in preparing lithographic printing plate not requiring dampening with water (hereinafter referred to as "a dry PS plate") is imagewise exposed to light by any known method, then the plate surface is rubbed with a sponge, nonwoven fabric, gauze or developing pad in the presence of a developer to remove the silicone rubber layer on the image areas of the plate and to thus give a lithographic printing plate not requiring dampening with water. When the development of an imagewise exposed PS plate is performed by an automatic developing machine, the silicone rubber layer on the image area of the plate has currently been removed by scrubbing away with 1 to 3 brush rollers positioned such that they come in contact with the surface of the plate while conveying the dry PS plate by rollers as disclosed in Japanese Unexamined Patent Publication (hereinafter referred to as "J.P. KOKAI") Nos. Sho 60-59351 and Sho 63-163357.
However, in the method for removing the silicone rubber layer by rubbing the plate surface with the developing pad, uneven force is inevitably applied to the plate surface. This is liable to result in uneven development and if a large number of dry PS plates are treated, the pad wears out and this requires a very long treating time and a great deal of labor.
Furthermore, the use of an automatic developing machine equipped with brush rolls suffers from severe problems of, for instance, reduction of half-tone dot reproducibility and occurrence of uneven development along the widthwise direction of the brush rolls due to wear or bending of the bristles of the brush rolls which becomes more serious as the number of processed PS plates is increased.